1. Technical Field
This disclosure generally relates to a method for calibrating medical diagnostic equipment, and more particularly, to a method for calibrating a thermal scanning system.
2. Description of the Related Art
Chiropractors and other health care professionals currently use devices to measure skin temperature at a variety of locations along a patient's spinal column. The purpose of taking such measurements is to monitor skin temperatures surrounding the spine. Imbalances in bilateral skin temperature readings may be indicative of abnormal autonomous nervous system activity, which in turn may indicate a spinal subluxation, or misalignment of adjacent vertebrae. Chiropractic care is directed toward locating and correcting subluxations by spinal adjustment. By creating a record of thermal readings paraspinally, i.e., along both left and right sides of a patient's spine, during the course of care, a chiropractor can quantitatively assess where subluxations exist, and how chiropractic care helps to alleviate them.
There are many commercially available medical devices capable of recording bi-lateral skin temperatures. One variety of these instruments utilizes two or more infrared thermal sensors mounted in a hand held unit which is rolled along a patient's spine. Two commercially available examples of such instruments are the “Insight Millennium Rolling Thermal Scanner” (Chiropractic Leadership Alliance, Mahwah, N.J.) and the “TyTron C-3000” (Titronics Research & Development, Oxford, Iowa).
In order to determine temperature imbalances along the spine, these instruments are rolled along the spine, and individual infrared thermal sensors independently measure the temperature on either side of the spine. Temperature differences of a few tenths of a degree Fahrenheit and/or Celsius are often considered clinically significant by clinicians.
The lynchpin in the theory of associating recorded temperature differences with actual skin temperature differences is the assumption that the two independent thermal sensors are precisely calibrated to one another throughout the full range of temperature readings. This is often not the case in practice, however, as the calibration of each of the thermal sensors can drift over time or be influenced by environmental conditions such as operating temperature and humidity.
In the real world, the clinicians who use these systems often must ask the question: “Is the measured temperature bilateral difference merely a result of calibration differences between adjacent sensors?” There are currently two principal field calibration techniques, which are described below with reference to the commercially available devices identified above.
The Insight Millennium Rolling Thermal Scanner uses a “synchronization” function in which the user separately points each of the two thermal sensors at a stable temperature source such as an easily identified location on a patient's back. Once each sensor is pointed that the exact same location, any differences in the sensor readings are automatically calculated as adjustments in the software calibration values. Disadvantages of this technique include: (1) potential error in having the user point each sensor at a spot with a stable temperature reading, and (2) potentially collecting data from patients using sensors that are not calibrated.
The Tytron C-3000 uses a calibration procedure in which the user modifies the calibration of the sensors by manually adjusting the software calibration values based on observations of repeated imbalances in that temperature data. Disadvantages of this technique include: (1) lack of an objective measurement basis to alter the calibration values, and (2) the likelihood of data collection from patients using sensors that have not been recently calibrated. The calibration method is also confusing, as illustrated by the portion of the instructions for a “Minor Calibration, Field Adjustment Procedure” taken from the Tytron C-3000 User Guide set forth below:                If the center graph (delta-T) readings seem to fall consistently to one side of the centerline the following adjustment in the scale factor for the opposite side will bring balance to zero. (If, for example, the scans seem to be slightly more to the right of the centerline, we would increase the temperature reading of the left probe to pull the average back to center.)        Scale Factors: Channel 0=calibration of LEFT barrel; Channel 2=calibration of RIGHT barrel        REDUCING the calibration number of the desired channel will INCREASE the temperature reading of that channel. REDUCING the number by 25 for example will increase the displayed temperature by approx. 0.5 degrees C.        EXAMPLE: If the center graph scans were all falling a bit to the left of center, we would want to increase the right probe's gain. We would therefore DECREASE the above scale factor for channel 2, thereby in-creasing the temperature of the right DT and “pull” the center reading towards centerline. For a small shift, subtract 10 from the example above and make channel 2's scale factor 1040. You may need to repeat this trial and error procedure after scanning 5 or 6 more patients and either take away more or add some back to bring balance to the center graph. A warning will appear when an attempt is made to change these settings, just click on “ok”.        
Thus, a need exists for a simple, easy to use, thermal calibration protocol and calculation in which the relative calibration of the two thermal sensors can be verified each time the system is utilized with a patient.